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Optical phase conjugator with spatially resolvable thresholding utilizing liquid crystal light valve
| Details |
Inventors: Pepper, David M.;
Assignee: Hughes Aircraft Company (Los Angeles, CA)
Primary Examiner: Miller; Stanley D.
Assistant Examiner: Gallivan; Richard
Attorney, Agent or Firm: Duraiswamy; V. D., Karambelas; A. W.
Apparatus is disclosed for phase conjugation of an input beam with thresholding of spatially resolvable parts of the beam that have amplitudes greater than a predetermined threshold value. A phase conjugation reflector produces a phase conjugated replica of a specularly reflected and thresholded portion of the input beam, which is retroreflected toward the source of the input beam. All of the spatial components of the phase conjugated replica retain the same relative phase relationships with respect to each other as the incident complex beam. In a preferred embodiment the invention comprises a liquid crystal light valve (LCLV) system, input and output polarizers, and a phase conjugate mirror (PCM). This combination of elements forms a device that can function as a threshold retroreflector with .about.10.sup.6 resolvable elements. Thresholding is accomplished by allowing part of each spatially resolvable component to reach the photoconductive layer on the opposite side of the LCLV dielectric mirror that reflects the component. The dielectric mirror can be made partially transmissive, or an optical feedback path can be provided to convey a portion of each spatially resolvable component to the photoconductive layer behind the point of reflection by the dielectric mirror. Various feedback methods are presented. The phase conjugate mirror can be implemented by means of any of the phenomena which give rise to phase conjugate retroreflection, such as stimulated scattering, stimulated photorefraction, three-wave mixing, or four-wave mixing. |
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DETAILED DESCRIPTION In view of the foregoing problems associated with the related art, it is a feature of the invention to implement a key element in an efficient all-optical associative memory.
It is another feature of this invention to provide a novel spatially resolving phase conjugator with a threshold characteristic.
In the accomplishment of these and other features of the invention, apparatus for phase conjugation of an input light beam is provided with thresholding of spatially resolvable parts of the beam.
A means for spatial light intensity modulation and specular reflection selects spatially resolvable components of the input beam that have amplitudes greater than a predetermined "hard" or "soft" threshold value.
A phase conjugation reflector retroreflects the complex conjugate of the selected spatially resolvable components which are incident on it.
As a result, a phase conjugated replica of a specularly reflected and thresholded portion of the input beam is retroreflected toward the source of the input beam.
Any general spatial light modulator may be employed.
In a preferred embodiment the invention comprises a liquid crystal light valve (LCLV) system operating in a display mode and in series with a phase conjugate mirror (PCM).
The PCM can be either a thresholding type or a nonthresholding type.
This combination of elements forms a device that can function as a threshold retroreflector with .
about.
10.
sup.
6 resolvable elements.
An input beam is first polarized and then reflected from the LCLV, which in combination with a second polarizer functions as a reflective, spatially addressable device with a "hard" or "soft" threshold.
The specularly reflected thresholded beam then strikes the PCM, which time-reverses the spatial components of the beam that are above the threshold set by the LCLV and the polarizers.
An input polarizing means polarizes the input beam before it strikes the liquid crystal light valve.
An output polarizing means is disposed in an optical path between the liquid crystal light valve and the phase conjugation mirror
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